      (* (nth (rotate-pi2 n_i) part)
 	(/ (- (square (Math/sin phi_0))
 	      (square (Math/sin phi_n_i)))
-	   (square (Math/sin phi_n_i)))))))
+	   (square (double (second n_i))))))))
 
 ;; Overall Energy and Force
 

     (* (nth (rotate-pi2 n_i) part)
        (/ (- (square (Math/sin phi_n_i))
	      (square (Math/sin phi_0)))
	   (square (Math/sin phi_n_i)))),

     (<= phi_0 phi_n_i (- Math/PI phi_0))
     0.0,

(defn- gravitative-force
  "Computes given part of gravitative force in layout on the
  inf-irreducible element n_i."
  [layout n_i part information]
  (let [upper-neighbours (:upper-neighbours-of-inf-irrs information),
	inf-irrs (:inf-irrs information),
